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May 1, 1962
w. D. ROWE
NOR LOGIC CIRCUIT HAVING DELAYED SWITCHING
3,032,664
AND EMPLOYING ZENER DIODE CLAMP
Filed May 16, 1958
WITNESSES
2 Sheets-Sheet 1
'
'
INVENTOR
William D. Rowe
ATTORNEY
May 1, 1962
‘
3 032
w. D. ROWE
NOR LOAGIES Ecnigggx'r HAVING DELAYED SWITCHING ’
_
'
Flled May 16, 1958
2 Sheets-Sheet 2
Fig. 4
D
————4—->
Delay-v
Tlme
Fig. 5
V
BEF
’664
YING ZENER DIODE CLAMP
Saturation 0f Collector
[Occurs Here
\ Inpui Resistance Curve
IBEF
Forward Bose-Emi?er Input Volrcqe vs
Forward Base-Emitter Input Current
_L_
(ZENER mom:
United States Patent U MEC€
1
3,032,664
Patented May 1, 1962
2
to delay the advanced pulse in a channel. This requires
special additional circuits.
It is an object of this invention to provide an improved
3,032,664
NOR LOGIC CIRCUIT HAVING DELAYED
SWITCHING AND EMPLOYING ZENER DI
logic circuit.
ODE CLAMP
It is another object of this invention to provide an im
William D. Rowe, Snyder, N.Y., assignor to Westing
proved NOR logic circuit capable of having a greater
number of multi-input-output connections than herein
house Electric Corporation, East Pittsburgh, Pa., a
corporation of Pennsylvania
Filed May 16, 1958, Ser. No. 735,796
8 Claims. (Cl. 307-885)
before was possible.
It is still another object of this invention to provide an
10 improved NOR logic circuit which contains therein time
This invention relates to logic circuitry in general,
and in particular to improved NOR logic circuits for
logic control systems.
The advent of logic circuits brought with them great
changes in the design of control systems for performing 15
delay provisions.
Further objects of this invention will become apparent
from the following description taken in conjunction with
the accompanying drawings. In said drawings, for illus
trative purposes only, there are shown preferred embodi
found great application in industrial control is the NOR
ments of the invention.
FIGURE 1 is a schematic diagram of a prior art NOR
logic circuit.
logic circuit;
all manner of functions.
One basic circuit which has
FIG. 2 is a schematic diagram of a ?rst embodiment of
In order to give a clear concept of the present inven
tion, a general statement of the logic on which the NOR 20 the teachings of this invention;
FIG. 3 is a second embodiment of the teachings of this
logic circuit is based follows. Assuming a voltage signal
is represented by one, and the absence of a voltage signal
invention;
'
FIG. 4 is a graphical representation of wave forms
is represented by zero, then a transistor NOR circuit may
present at selectedpoints of the apparatus illustrated in
be expressed logically in the binary" number system. The
’
binary number system is based on a radix of 2 instead of 25 FIG. 3;
FIG. 5 is a graphical representation of a characteristic
a radix of 10 as in the decimal system. Therefore, only
of a transistor device which may be employed in the
two numbers, zero and one, are required to form the
apparatus of FIGS. 2 and 3; and
combinations to represent all numbers. Following this
system, a transistor NOR circuit provided with two inputs
FIG. 6 is a third embodiment of the teachings of this
which we will designate A and B, may be analyzed in the 30 invention.
following manner.
Referring to FIG. 1, the NOR logic element comprises
a transistor having three electrodes shown generally at 10.
(1) If input A is zero and input B is zero, then an out
put C is one.
In this particular embodiment of the invention, a PNP
transistor is employed, however, it is to be understood
(2) If input A is zero and input B is one, the output C
is zero.
35 that an NPN transistor may also be utilized by reversing
the polarity of the bias and signal voltages. Further,
(3) If input A is one and input B is zero, then output C
both germanium and silicon transistors have been em
is zero.
ployed with success. The transistor 10 is to be used in
(4) If input A is one and input B is one, then output C
a switching mode. That is, an input signal applied be
is zero.
These four provisions may be combined in one state 40 tween two of said three electrodes will be of su?icient
magnitude to drive said transistor to saturation. A bias
ment. The output C is one only if neither input A not
or supply voltage will be connected between a third and
input B is one. The key word in this statement is NOR,
one of said two electrodes.
which expresses both a logic operation and negation.
The PNP transistor 10 is provided with a base electrode
Therefore, this circuit is termed a NOR circuit and the
logic will be called NOR logic.
45 11, a collector electrode 12 and an emitter electrode 13.
The greater the number of inputs and outputs of a logic
The NOR circuit element is provided with output ter
minals 14 and 15 across which a load 16 is connected.
circuit, the more versatile, flexible and economic it is.
It can be shown in general, that fewer multi-input-output
As shown the collector 12 is connected to the output ter
logic circuits are required in designing logic networks than
minal 14. The emitter 13 is connected to the output ter
for logic circuits with a smaller number of inputs and out 50 minal 15. The emitter 13 is also connected to ground.
A plurality of input terminals 20, 21, 22 and 23 are
puts. Also, in designing logic circuits for switching func
tions, more than just the logic must be considered. The
timing functions of each circuit in operation must be espe
cially known. In switching a logic circuit of any'type, a
provided.
The terminal 23 is the return terminal and is
connected to ground.
Resistors and diodes are shown
connected between the input terminals 20, 21 and 22 and
?nite time interval occurs in the switching from one state 55 the base electrode 11. Diodes are shown and described
in the modi?cations of this application and they serve to
of the circuit to the complementary state of the circuit.‘
improve the isolation of the circuits but they may be
A pulse is formed by turning a logic circuit on for a short
dispensed with and proper functioning of the circuits
time interval and then turning it off. The pulse thereby
obtained.
formed has a ?nite delay caused by the interval required
In this embodiment of the NOR circuit element, a re
for the rise and fall time of the pulse. This delay is with 60
respect to the input pulse initiating the switching. There
sistor 25 and a diode 26 are connected in series circuit
fore, in logic circuits where switching occurs in sequence,
relationship between the input terminal 20 and the base
these delays can add up even though they are very short
electrode 11. Resistor 27 and diode 28 are connected in
to begin with. Unequal delays in two channels which
connect any point further along in the logic system means
series circuit relationship between the input terminal 21
that a “racing” condition will occur. That is, informa
tion in one channel will reach the junction point before
information from the other channel will. This “racing”
leads to erratic errors in the logic system. In order to
nected between the input terminal 22 and the base elec
and base electrode 11. Resistor 29 and diode 30 are con
trode 11.
A source of power 32 is provided and connected
through an impedance 33 to the collector 12. Since a
eliminate this “racing” in these logic circuits, time delays 70 PNP transistor is used in this embodiment of the inven
must be inserted in various positions in the logic system
tion, the source of power for supplying a bias voltage
3,032,664
on the collector 12 will be disposed to deliver negative
bias voltage. The voltage rating of the power source 32
will depend upon the conditions to be met in the logic
circuit and the characteristics of the transistor 10.
A
temperature compensating network, including a tempera
ture sensitive resistor 35 and a voltage source 34, is con
nected in series loop circuit relationship with the base
electrode 11 and the emitter electrode 13 which emitter
electrode is connected to ground.
Jib
The gain of the transistor 10 must be regulated at this
current.
It can be shown that for one input and negligible leak
age current for the transistor 10, that the number of out
puts of the NOR circuit is exactly equal to the gain of
the circuit if the source collector impedance is considered
in?nite. This arises from the fact that, if there is no
leakage (no temperature compensations required), no in
put current drain from auxiliary input, and the voltage
source dynamic impedance is in?nite, the amount of out
put current (Io) that is available to drive succeeding cir
cuits is exactly equal to the current (1,) that the tran
sistor may conduct during saturation, i.e. 10:15. An out
A NOR logic element of this type is described in
greater detail in a copending application Serial No.
628,331, entitled “Temperature Compensating Devices for
NOR Elements for Control Systems,” ?led December 14,
put drives a similar circuit which requires an input cur
1956, and assigned to the same assignee as the present
rent (lj) equal to the current switched during saturation
invention.
15
divided by the gain (B) of the circuit, i.e.
Referring to FIG. 2, there is illustrated .an embodiment
of the teachings of this invention in which like com
I 8 ID
ponents of FIGS. 1 and 2 have been given the same
reference characters. The main distinction between the
apparatus illustrated in FIGS. 1 and 2 is that a diode 20 It then follows that the output current is then sufficient
clamp network has been connected across the emitter 13
to drive a number of succeeding inputs which is exactly
and collector 12 of the transistor 10. The clamp network
equal to the transistor gain, i.e.
comprises a voltage source 43, a resistor 42 and a recti?er
“a”?
41 connected in series circuit relationship.
5
It can be shown mathematically that all logic, exclu 25
Ii
sive of Memory logic, can be performed on two levels,
if an in?nite number of inputs and outputs to a logic
IO/IJ is also the ratio of current available to current drain
circuit are available. This means that in many cases
for one input. In practice, it is possible to drive a circuit
fewer logic circuits are required to perform logic func
with the number of outputs equal to about half the gain
tions than needed otherwise. If a logic circuit can be 30 of the transistor 10 with as many inputs. Therefore, a
made to accommodate more inputs and more outputs
practical NOR circuit, according to this invention, and
without harming the operation and sizably increasing the
considering a transistor with a gain of 50, may have in
cost, it would therefore be more economical to do so.
the order of 25 inputs and 25 outputs. This is a great
The diode clamp network 40 connected across the output
improvement in versatility over the NOR circuit appara
of the NOR circuit illustrated in FIG. 2 does not inter 35 tus as illustrated in FIG. 1.
fere with the operation or logic of the NOR circuit and
It is desirable to make this source collector impedance
is quite economical. However, it allows the NOR circuit
look like a constant current source. Therefore, the value
of FIG. 2 to have a much higher number of inputs and
of the voltage source 32 must be much greater than the
outputs than the ordinary NOR circuit hereinbefore de
value of the voltage source 43 and the resistance of the
scribed. The multi-input NOR circuit is a prime require 40 resistor 42, equivalent resistance of the diode 41, must
ment in control circuits, and is becoming practically an
be as small as possible. The recti?er diode 41 should
absolute necessity in digital computer circuits. In addi
tion, it is evident that the multi-input NOR circuit of FIG.
2 having the added diode clamp network 40 and the
essentially be a high-back impedance, low-forward im
pedance diode. It may preferably be of the junction type.
Referring to FIG. 6 there is illustrated another embodi
ordinary NOR circuit illustrated in FIG. 1 will be com 4.5 ment of the teachings of this invention, in which like
components of FIGS. 2 and 6 have been given the same
patible with one another.
‘
Referring again to FIG. 2, the series resistor 42 and
reference characters. The main distinction between the
the recti?er diode 41 are connected from the voltage
apparatus illustrated in FIGS. 2 and 6 is that in FIG. 6
source 43 to the collector 12 of the transistor 10. The
a Zener-type diode 44 has been substituted in the diode
diode 41 is polarized so that the cathode side of the diode 50 clamp network 40 for the diode 41, equivalent resistor 42
is connected directly to the collector 12 of the transistor
and the voltage source 43 of FIG. 2.
10. The voltage source 43 is to have a magnitude sut?
The recti?er diode 44 is of the type that has a Zener
cient to drive a succeedingytransistor into saturation,
type breakdown in the reverse direction. If the recti?er
through an input resistance of the succeeding transistor.
diode 44 is of the Zener type, the voltage source 43 may
The magnitude of the voltage source 32 is much greater 55 be eliminated. If the Zener type diode is used for recti
than that of the voltage source 43 and may be chosen
?er 41 the polarity of the diode 44 must be reversed
to be between 10 to 20 times the magnitude of the volt
compared to diode 41. For the same operation of the
age source 43. This high voltage from the voltage source
logic circuit hereinbefore described, the critical breakdown
32 through the resistor 33 in effect supplies a constant
voltage of the Zener type diode 44 would be the same as
current to the collector 12 of the transistor 10. How 60 the magnitude of the omitted voltage source 43. Thus
the diode 43 would break down in the reverse direction
ever, because of the recti?er diode 41, which is biased
and maintain a substantially constant potential between
at the value of the voltage source 43, the collector 12 of
the emitter electrode 13 and the collector electrode 12.
the transistor 10, or the potential between the two elec
Referring to FIG. 3, there is illustrated another embodi
trodes 12 and 13, can never exceed the value of the volt
age source 43. Therefore, the collector 12 of the tran 65 ment of the teachings of this invention, in which like com
ponents of FIGS. 2 and 3 have been given the same refer
sistor 10, during the time the transistor 10 is cut off, acts
ence characters. The main distinction between the ap
paratus illustrated in FIGS. 3 and 2 is that in FIG. 3, a
nitude of the voltage source 43, to the load to be con
capacitance or electrical energy storage means 50 has been
nected to the output terminals. Therefore, one can drive
a great number of outputs to succeeding stages from this 70 connected directly between the emitter 13 and the base 11,
or the two input electrodes, of the transistor 10.
constant source output.
As discussed hereinbefore, unequal delays in two logic
It should be noted that when the transistor 10 is in
channels which connect at any point further along in the
saturation, it sees a current equal to the magnitude of
logic system means that a “racing” condition will occur.
the voltage source 32 divided by the resistance of the
That is, information in one channel will reach the junc
resistor 33 through the emitter 13 and the collector 12.
as though it were a constant current source, at the mag
3,032,664
6
age source having a voltage magnitude at least two times
tion point before information from the other channel
will. This racing leads to erratic errors in the logic sys-_
tern. In order to eliminate this “racing” in these logic
circuits, time delays must be inserted in various positions
in the logic system to delay the advanced pulse in a chan
nel. This requires special additional circuits. The con
nection of the capacitor 50 across the emitter 13 and
greater than said critical breakdown potential.
2. In a logic circuit, in combination; a transistor hav
ing three electrodes; means for applying an input signal
between two of said electrodes; means connecting a volt
age source between a third and one of said two electrodes;
and a diode clamp circuit comprising a Zener-type diode
serially connected between said third and said one of said
two electrodes; said voltage source and said Zener-type
the base 11 of the transistor 10 delays the NOR circuit
input pulses by a ?nite time interval. Addition of the
capacitor 50 causes the NOR circuit to function as its own 10 diode being poled such that the potential between said
third and said one electrode can never exceed the break
delay line.
down potential of said Zener-type diode; said voltage
Referring to FIG. 4, the pulses X would be the ordi
nary output of the NOR circuit without the capacitor 50
source having a voltage magnitude at least two times
attached. By connecting the capacitor 50 into the circuit,
the new pulse output Y is shown with the actual time
delay D also shown in FIG. 4. The novel mechanism
involved is the use of the non-linear features of the base
emitter diode of the transistor 10. A graphical repre
sentation of this input resistance curve is shown in FIG. 5.
The representation of FIG. 5 plots the forward base—
emitter input voltage of the diode versus the forward
base-emitter input current of the diode. As shown, a
de?nite break-point occurs at the point where collector
saturation begins. This is the basis for operation of the
circuit.
In operation, the capacitor 50 is charged up to the
base resistance of the transistor 10 by an input pulse ap
plied to one of the plurality of input terminals. The volt
age on the base of the transistor 10 increases exponen
tially with time. After an interval, which is the interval
of delay, the voltage of the base of the transistor 10
reaches the point where the transistor can be saturated.
15
greater than said breakdown potential of said Zener-type
diode; said breakdown potential having a magnitude suiti
cient to drive a transistor of a succeeding network into
saturation; said Zener-type diode being poled in the op
posite direction across said third and one electrode as said
voltage source.
20
3. In a logic circuit, in combination; a transistor hav
ing three electrodes; means for applying an input signal
between two of said electrodes; means connecting a volt
age source between a third and one of said two electrodes;
a capacitor means directly connected between said two
25 electrodes of said transistor; and a diode clamp circuit
comprising a Zener-type diode serially connected between
said third and said one of said two electrodes; said voltage
source and said Zener-type diode being poled such that
the potential between said third and said one electrode can 30 never exceed the breakdown potential of said Zener-type
diode; said voltage source having a voltage magnitude
much greater than said breakdown potential of said Zener
type diode.
When the transistor 10 swings into saturation, the base
resistance of the transistor 10 switches to a very low
4. In a logic circuit, in combination; a transistor having
resistance. The capacitor 50 then begins to discharge 35 three electrodes; means for applying an input signal be
through the base resistance of the transistor 10 after the
tween two of said electrodes; means connecting a voltage
input pulse ends. The voltage on the base resistance of
source between a third and one of said two electrodes; a
the transistor 10 now decreases exponentially. When the
capacitor means connected between said two electrodes of
voltage on the base of the transistor 10 reaches the point
said transistor; and a diode clamp circuit comprising a
where it can no longer hold the transistor 10 in satura 40 Zener-type diode serially connected between said third
tion, the transistor 10 switches back to the cut-off state.
and said one of said two electrodes; said voltage source
Since the voltage swings at the base of the transistor 10
and said Zener-type diode being poled such that the po
are quite large as compared to that required to drive the
tential between said third and said one electrode can
transistor 10 into saturation, the rise and fall time of the
never exceed the breakdown potential of said Zener-type
pulses which correspond to the linear region of the tran~
diode; said voltage source having a voltage magnitude
sistor 10 operation are quite sharp. The delay time D
much greater than said breakdown potential of said Zener
is varied by correct choice of the shunting capacitor 50.
type diode; said Zener-type diode having a breakdown po
The modi?ed embodiment of the NOR logic circuit as
tential of a magnitude su?’icient to drive a transistor of a
illustrated in FIG. 3 is very useful in the construction of
succeeding network into saturation.
logic systems using the NOR function. The addition of 50
5. In a logic circuit, in combination; a transistor hav
the capacitor 50 does not change the NOR logic, but
simply adds a contro ldelay at the appropriate position
in the logic system. The important feature is that, al
though use of capacitor for delay by integration means
is well known, the method used here uses the non-linear
resistance of the transistor 10 input in conjunction with
the capacitor 50 to afford a time delay for the NOR cir
cuit without interfering with the wave form. This is a
novel application of this non-linear resistance.
In conclusion, it is pointed out that while the illustrated
examples constitute practical embodiments of my inven
tion, I do not limit myself to the exact details shown,
since modi?cation of the same way be varied without
departing from the spirit and scope of this invention.
I claim as my invention:
1. In a logic circuit, in combination; a transistor having
three electrodes; means for applying an input signal be
tween two of said electrodes; means connecting a volt
age source between a third and one of said two electrodes;
and a diode clamp circuit comprising a Zener-type diode
serially connected between said third and said one of said
two electrodes; said voltage source and said Zener-type
diode being poled such that the potential between said
third and said one electrode can never exceed the critical
ing three electrodes; means for applying an input signal
between two of said electrodes; means connecting a volt
age source between a third and one of said two electrodes;
a capacitor connected directly between said two electrodes
of said transistor; and a diode clamp circuit comprising a
Zener-type diode serially connected between said third and
said one of said two electrodes; said voltage source, and
said Zener-type diode being poled such that the potential
between said third and said one electrode can never ex~
ceed the breakdown potential of said Zener-type diode;
said voltage source having a voltage magnitude at least
two times greater than the breakdown potential of said
Zener-type diode; said Zener-type diode having a break
down potential of a magnitude sufficient to drive a tran
65 sistor of a succeeding network into saturation; said Zener
type diode being poled in the opposite direction across
said third and one electrode as said voltage source.
6. In a logic circuit, in combination; transistor means
having base, emitter and collector electrodes; means for
applying an input signal between said base and emitter
electrodes; means connecting a voltage source between
said emitter and collector electrodes; and a diode clamp
circuit comprising a Zener-type diode connected between
said emitter and collector electrodes; said voltage source
breakdown potential of said Zener-type diode; said volt 75 and said Zener-type diode being poled so that the poten
3,032,664
7
tial between said emitter and collector electrodes never
exceeds the value of the breakdown potential of said
Zener-type diode; said voltage source having a magnitude
at least two times greater than said breakdown potential.
7. In a logic circuit, in combination; transistor means
having base, emitter and collector electrodes; means for
applying an input signal between said base and emitter
5
a series connected voltage source of a selected relatively
high value, to drive a transistor of a succeeding network
into saturation connected across the collector and the
ground to thus be connected across the collector and
emitter; a diode clamp circuit connected across the col
lector and emitter and having characteristics to maintain
the collector voltage constant at a relatively low voltage
value during the cut-oil’ condition of the transistor; and a
capacitor connected directly across the base and emitter
electrodes; means connecting a voltage source between
said emitter and collector electrodes; and a diode clamp
circuit comprising a Zener-type diode connected between 10 to provide pulse time delay for pulse signals applied across
the base and emitter.
said emitter and collector electrodes; said voltage source,
and said Zener-type diode being poled so that the potential
between said emitter and collector electrodes never ex
ceeds the value of the breakdown potential of said Zener
type diode; said voltage source having a magnitude at 15
least two times greater than said breakdown potential;
said Zener-type diode having a potential of a breakdown
magnitude sufficient to drive a transistor of a succeeding
network into saturation; said Zener-type diode being poled
the opposite direction across said emitter and base elec 20
trodes as said voltage source.
8. In a logic circuit, in combination; a transistor hav
ing a base electrode, a collector electrode, and a grounded
emitter electrode; circuit means, including a resistor and
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,603,746
2,845,548
Burkhart ____________ __ July 15, 1952
Silliman et a1. ________ __ July 29, 1958
2,880,330
2,892,103
Linvill ______________ __ Mar. 31, 1959
Scarbrough __________ __ June 23, 1959
OTHER REFERENCES
A Digital to Analogue Shaft Converter, by Harry
Margulius and Paul M. Cable, a thesis submitted at the
Massachusetts Institute of Technology, June 1957, pub
lished March 1, 1956, pages 47 and 49.